More Strength, Less Weight

Steel-reinforced concrete is a mainstay of the building industry throughout the world, but it could someday be supplanted by concrete reinforced with carbon fibers. In Germany, the Carbon Concrete Composite Project, known as Project C3, is pursuing the possibilities of this enhanced building material with the construction of the CUBE, a 2,368-square-foot structure made almost entirely with carbon fiber-reinforced concrete.

Funded by Germany’s Federal Ministry of Education and Research, Project C3 is a consortium of 160 science and industry partners that have been working together since 2014 to develop materials and technologies for carbon fiber-reinforced concrete. TU Dresden, a public research university and a Project C3 partner, is leading the design and construction of the CUBE.

Built on the Fritz-Förster-Plat square in Dresden, the CUBE will be an experimental building where researchers can study the suitability of carbon fiber-reinforced concrete from construction, structural and building physics viewpoints. The building’s two carbon fiber-reinforced sections include the box, which is a two-story modular building, and the twist shells, featuring two identical, double-curved structures turned 180 degrees to each other. A steel and glass façade will connect the twists and the box.

The precast concrete box is being manufactured in an automated concrete plant and should be ready by early fall. The twists will be produced on the building site, using the wet spraying method of concrete construction.

“The twists perform the function of both supporting shell and weather shell,” says Manfred Curbach, director of the Institute for Concrete Structures at TU Dresden. The shell structures, just 1.5 inches thick, are designed to use as little concrete as possible. They are made with double-layered carbon reinforcements, with thin concrete webs on top of them.

“Extruded polystyrene (XPS) foam blocks are integrated between these webs, which run both lengthwise and crosswise. The pre-formed XPS blocks provide thermal insulation and reduce weight,” says Curbach. “A further layer of 4-centimeter carbon-reinforced concrete is placed over this layer and seals the entire surface. This structure forms the whole supporting shell of the twist element.”

After that comes a full-surface polyurethane foam insulation, which is also sealed. The final layer is a 1.2 to 1.5-inch shell of white concrete, installed without joints. The supporting shell and the weather shell are connected by glass fiber reinforcement bars.

Current plans are to have the box on site and the two twist shells completed by the end of February 2021. Construction of the steel and glass façade and installation of building services will follow, with an anticipated completion date of June 2021.